Steady-State and Transient Currents in Organic Liquids by Injection from a Tunnel Cathode

Experimental data are presented on the currents induced in organic liquids by injection from a tunnel cathode. The injection level was varied over a wide range resulting in almost no space‐charge limitation to almost complete space‐charge limitation. Results were different from that usually observed in solids, in that at low fields, the steady‐state current was proportional to V², while at high fields the current was proportional to V. By proper choice of electrode spacing and applied voltage, space‐charge‐limited current transients as low as 10⁻¹¹ A∕cm² and 5 sec transit times were observed. A smooth transition between the electrode‐limited and the space‐charge limited regimes was achieved by varying the junction voltage that varied the injection level

Hot electron injection into dense argon, nitrogen, and hydrogen

Hot electrons have been injected into very dense argon, nitrogen, and hydrogen gases and liquids. The current‐voltage characteristics are experimentally determined for densities (N) of argon, nitrogen, and hydrogen ranging from about 10²⁰ to 10²² cm⁻³ and applied fields (E) ranging from about 10 to 10⁴ V cm⁻¹. The argon data show a square root E∕N dependence of the current. The nitrogen and hydrogen data show a complicated dependence of the current on E∕N due to the rapid thermalization in the region of the image potential of the injected electrons through inelastic collision processes not present in argon. A hydrodynamic‐two‐fluid model is developed to analyze the nitrogen and hydrogen data. From the analysis of our data, we obtain the density dependence of the momentum exchange scattering cross section and the energy relaxation time for the injected hot electrons

New Thin-Film Tunnel Triode Using Amorphous Semiconductors

A new thin‐film tunnel triode is discussed which uses a p‐type amorphous film to achieve amplification of injected current from a tunnel cathode. It is not only the basis for a new semiconductor device but also suggests a novel method for measuring electrical properties of semiconductors

Erratum: Environmental Swap Energy and Role of Configurational Entropy in Transfer of Small Molecules from Water into Alkanes

Presents correction to an article related to configurational entropy in transfer of small molecules from water into alkanes, published in the 2005 issue of The Journal Chemical Physics and is available online at: http://archives.pdx.edu/ds/psu/836

Comment on Electron Scattering in the Image Potential Well

Comments are made on the model of electron injection into SiO₂ proposed by Berglund and Powell. Their assumptions on electron scattering, disregarding the change of the escape cone with the distance from the emitter, lead to serious underestimation of the injected current. Two alternative models of electron injection, based solely on elastic scattering are discussed and do not predict the experimental results. We suggest that observed field dependence of the injected current into SiO₂ indicates that energy relaxation associated with the injected electrons is responsible for the voltage dependence of the current

Environmental Swap Energy and Role of Configurational Entropy in Transfer of Small Molecules from Water into Alkanes

We studied the effect of segmented solvent molecules on the free energy of transfer of small molecules from water into alkanes (hexane, heptane, octane, decane, dodecane, tetradecane, and hexadecane). For these alkanes we measured partition coefficients of benzene, 3-methylindole (3MI), 2,3,4,6-tetrachlorophenol (TeCP), and 2,4,6-tribromophenol (TriBP) at 3, 11, 20, 3, and 47 °C. For 3MI, TeCP, and TriBP the dependence of free energy of transfer on length of alkane chains was found to be very different from that for benzene. In contrast to benzene, the energy of transfer for 3MI, TeCP, and TriBP was independent of the number of carbons in alkanes. To interpret data, we used the classic Flory–Huggins (FH) theory of concentrated polymer solutions for the alkane phase. For benzene, the measured dependence of energy of transfer on the number of carbons in alkanes agreed well with predictions based on FH model in which the size of alkane segments was obtained from the ratio of molar volumes of alkanes and the solute. We show that for benzene, the energy of transfer can be divided into two components, one called environmental swap energy (ESE), and one representing the contribution of configurational entropy of alkane chains. For 3MI, TeCP, and TriBP the contribution of configurational entropy was not measurable even though the magnitude of the effect predicted from the FH model for short chain alkanes was as much as 20 times greater than experimental uncertainties. From the temperature dependence of ESE we obtained enthalpy and entropy of transfer for benzene, 3MI, TeCP, and TriBP. Experimental results are discussed in terms of a thermodynamic cycle considering creation of cavity, insertion of solute, and activation of solute-medium attractive interactions. Our results suggest that correcting experimental free energy of transfer by Flory–Huggins configurational entropy term is not generally appropriate and cannot be applied indiscriminately. An Erratum has been published and is located here: http://archives.pdx.edu/ds/psu/836

Cryogenic thin-film electron emitters

Thin‐film electron emitters are described, which operate below 200°K and below a limiting critical applied voltage (νc) in a stable temperature‐independent regime. Current‐voltage characteristics and normal electron energy distributions are presented. Fabrication and operation criteria are outlined. Comparison with temperature‐dependent emitters is made, and possible conduction mechanisms discussed briefly

Hot Electron Injection into Liquid Argon from a Tunnel Cathode

Hot electrons from a tunnel cathode have been injected into liquid argon (99.998% pure) at 87°K. The current vs voltage characteristics indicate that the injected hot electrons thermalize very slowly, losing their energy only by elastic scattering processes and finally by capture by the dilute impurities. The deduced thermalization time and distance are very long compared with that in helium, where bubble formation is responsible for energy loss

Electrophoretic mobility of sarcoplasmic reticulum vesicles — Analytical model includes amino acid residues of A+P+N domain of Ca2+-ATPase and charged lipids

AbstractThis work is an experimental and theoretical study of electrostatic and hydrodynamic properties of the surface of sarcoplasmic reticulum (SR) membrane using particle electrophoresis. The essential structural components of SR membrane include a lipid matrix and a dense layer of Ca2+-ATPases embedded in the matrix. The Ca2+-ATPase layer both drives and impedes vesicle mobility. To analyze the experimental mobility data, obtained at pH4.0, 4.7, 5.0, 6.0, 7.5, and 9.0 in 0.1M monovalent (1:1) electrolyte, an analytical solution for the vesicle mobility and electroosmotic flow velocity distribution was obtained by solving the Poisson–Boltzmann and the Navier–Stokes–Brinkman equations. The electrophoretic mobility model includes two sets of charges that represent: (a) charged lipids of the lipid matrix of the vesicle core, and (b) charged amino acid residues of APN domains of Ca2+-ATPases. APN domains are assumed to form a charged plane displaced from the surface of lipid matrix. The charged plane is embedded in a frictional layer that represents the surface layer of calcium pumps. Electrophoretic mobility is driven by the charged APN domain and by lipid matrix while the surface layer provides hydrodynamic friction. The charge of APN domain is determined by ionized amino acid residues obtained from the amino acid composition of SERCA1a Ca2+-ATPase. Agreement between the measured and the predicted mobility is evaluated by the weighted sum of mobility deviation squared. This model reproduces the experimental dependence of mobility on pH and predicts that APN domains are located in the upper half of the SR vesicle surface layer

Electrophoretic Mobility of Sarcoplasmic Reticulum Vesicles is Determined by Amino Acids of A + P + N Domains of Ca2+–ATPase

Establishing the origin of electrophoretic mobility of sarcoplasmic reticulum (SR) vesicles is the primary goal of this work. It was found that the electrophoretic mobility originates from ionizable amino acids of cytoplasmic domains of the Ca2+–ATPase, the calcium pump of SR. The mobility was measured at pH 4.0, 4.7, 5.0, 6.0, 7.5, and 9.0 in the region of ionic strength from 0.05 to 0.2 M. Mobility measurements were supplemented by studies of SR vesicles by photoelectron microscopy. The median diameter of SR vesicles was 260 nm. Ca2+–ATPases were not resolved. The mobility data were standardized by interpolation to a reference ionic strength of 0.1 M. The mobility of the SR vesicles is determined by the charge of the Ca2+–ATPase. It is due to the ionizable amino acids selected from the amino acid sequence of SERCA1a Ca2+–ATPase. The pH dependence of charge residing in various domains of Ca2+–ATPase was computed using pKa values in free water. The charge correlated with measured mobility. It was shown that a linear relationship exists between the mobility of the SR vesicles, μ, and the total computed charge, Q, on three cytoplasmic domains of Ca2+–ATPase: A, P, and N. It is given by μ = α + β Q where the fitted values β = (0.043 ± 0.002) × 10−8 m2 V−1 s−1 e−1 and α = (0.16 ± 0.02) × 10−8 m2 V−1 s−1. Since β and α values do not change from pH 4 to pH 9, one concludes that the hydrodynamic friction of the cytoplasmic domains of SR is independent of their charge